Carbon nanotubes are unique carbon-based, molecular structures that exhibit interesting and useful electrical properties. Two general types of carbon nanotubes are referred to as multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs). SWNTs have a cylindrical sheet-like, one-atom-thick shell of hexagonally-arranged carbon atoms, and MWNTs are typically composed of multiple coaxial cylinders of ever-increasing diameter about a common axis. Thus, SWNTs can be considered to be the structure underlying MWNTs and also carbon nanotube ropes, which are uniquely-arranged arrays of SWNTs.
Carbon-based nanotubes are being studied for implementation in a variety of applications. These applications include, among others, chemical and bio-type sensing, field-emission sources, selective-molecule grabbing, nano-electronic devices, and a variety of composite materials with enhanced mechanical and electromechanical properties. More specifically, for example, in connection with chemical and biological detection, carbon nanotubes are being studied for applications including medical devices, environmental monitoring, medical/clinical diagnosis and biotechnology for gene mapping and drug discovery. For general information regarding carbon nanotubes, and for specific information regarding SWNTs and their applications, reference may be made generally to “Carbon Nanotubes: Synthesis, Structure, Properties and Applications,” M. S. Dresselhaus, G. Dresselhaus and Ph. Avouris (Eds.), Springer-Verlag Berlin Heidelberg, New York, 2001; and “T. Single-shell Carbon Nanotubes of 1-nm Diameter,” IIJIMA, S. & Ichihashi, Nature 363, 603–605 (1993).
Sensing molecular, chemical and biological species plays an important role in many industrial, agricultural, medical, and environmental processes. Detection of toxic gases, for example, provides a crucial measure of environmental pollution. In addition, detecting molecular concentrations can be useful in a variety of sensing and other applications. However, previously-available nanotubes have been difficult to manufacture and implement in a variety of such applications.